1. Field of the Invention
This invention relates to a degradation determining system and method for an exhaust gas sensor and an engine control unit, which determine degradation of the exhaust gas sensor based on an output from the exhaust gas sensor, the exhaust gas sensor outputting a signal indicative of the amount of a predetermined component contained in exhaust gases emitted from an internal combustion engine into an exhaust passage thereof.
2. Description of the Related Art
Conventionally, a degradation determining system of the aforementioned kind has been disclosed e.g. in the publication of Japanese Patent No. 2978960 (seventh column at page 4 to fifteenth column at page 8, and FIG. 3 and FIGS. 7 to 10). This degradation determining system determines degradation of an air-fuel ratio sensor that outputs a signal indicative of a sensed concentration of oxygen contained in the exhaust gases. The degradation of the air-fuel ratio sensor is determined during feedback control of the air-fuel ratio of a mixture supplied to the engine, which is provided in response to an output from the air-fuel ratio sensor. More specifically, when the output from the air-fuel ratio sensor assumes, for example, a richer value than a threshold value equivalent to a stoichiometric air-fuel ratio, an air-fuel ratio correction coefficient for controlling the air-fuel ratio of the mixture is decremented each time by a predetermined value, whereby the air-fuel ratio of the mixture is progressively changed in the leaning direction. Then, after a time point the output from the air-fuel ratio sensor crosses the above threshold value in the leaning direction, the control of the air-fuel ratio is held at the resulting state until a predetermined time period elapses. Upon the lapse of the predetermined time period, the air-fuel ratio correction coefficient starts to be incremented each time by a predetermined value, whereby the air-fuel ratio is changed in the enriching direction. Then, after a time point the output from the air-fuel ratio sensor crosses the above threshold value in the enriching direction, the state of control of the air-fuel ratio is held at the resulting state until a predetermined time period elapses. The above air-fuel ratio control for changing the air-fuel ratio in the leaning direction and then in the enriching direction is repeatedly carried out to see if the cycle of changes in the output from the air-fuel ratio sensor during provision of the above-described air-fuel ratio control is equal to or larger than a predetermined reference value, and when the cycle is equal to or larger than the predetermined reference value, it is determined that the air-fuel ratio sensor is degraded.
However, according to the above conventional degradation determining system, the air-fuel ratio is progressively increased and decreased, and therefore, during execution of the degradation determining process, if the opening degree of the throttle valve is changed due to an unintended slight change in the degree of depression of an accelerator pedal by the driver, the fuel injection amount is increased or decreased in response thereto to cause changes in the air-fuel ratio. This changes the cycle of changes in the output from the air-fuel ratio sensor. Further, there is a case in which even with the same fuel injection amount, the actual air-fuel ratio can vary due to variation in adhesion properties of fuel. In such a case as well, the output from the air-fuel ratio sensor undergoes changes in the cycle. If noise caused by such unexpected changes in the air-fuel ratio during provision of the above-described control of the air-fuel ratio is mixed into the output from the air-fuel ratio sensor, there is a fear that the accuracy of the determination of degradation of the air-fuel ratio sensor is lowered.
It is an object of the present invention to provide a degradation determining system and method for an exhaust gas sensor and an engine control unit, which are capable of determining degradation of the exhaust gas sensor, while suppressing influence of noise caused by unexpected changes in the air-fuel ratio of a mixture on the output from the exhaust gas sensor during provision of control of the air-fuel ratio, thereby enhancing the accuracy of the determination of degradation of the exhaust gas sensor.
To attain the above object, in a first aspect of the present invention, there is provided a degradation determining system for an exhaust gas sensor, for determining degradation of the exhaust gas sensor based on an output from the exhaust gas sensor, the exhaust gas sensor outputting a signal indicative of an amount of a predetermined component contained in exhaust gases emitted from an internal combustion engine into an exhaust passage thereof,
the degradation determining system comprising:
determining input-generating means for generating a determining input for determining degradation of the exhaust gas sensor;
modulation output-generating means for generating a modulation output by modulating the generated determining input, using any one of a xcex94xcexa3 modulation algorithm, a xcexa3xcex94 modulation algorithm, and a xcex94 modulation algorithm;
control means for controlling an amount of fuel to be injected into the engine, according to the generated modulation output; and
degradation determining means for determining degradation of the exhaust gas sensor based on the output from the exhaust gas sensor delivered when the amount of fuel to be injected is controlled by the control means.
With the arrangement of the degradation determining system according to the first aspect of the present invention, a determining input for determining degradation of the exhaust gas sensor is modulated using any one of the xcex94xcexa3 modulation algorithm, the xcexa3xcex94 modulation algorithm, and the xcex94 modulation algorithm, thereby generating a modulation output. The amount of fuel to be injected into the engine (fuel injection amount) is controlled according to the generated modulation output, and at the same time degradation of the exhaust gas sensor is determined based on the output from the exhaust gas sensor delivered when the fuel injection amount is controlled by the control means. The above-mentioned three modulation algorithms output a signal indicative of a value of +1 or a value of xe2x88x921, and therefore, by setting the gain of the modulation output to an appropriate value, the fuel injection amount can be varied with a relatively large amplitude. This makes it possible to vary the fuel injection amount with a larger amplitude than a range of changes in the fuel injection amount causing the unexpected changes in the air-fuel ratio described hereinabove. This makes it possible to make the unexpected changes in the air-fuel ratio obscure or lost in changes in the air-fuel ratio the range of which is controlled by the above-described control of the fuel injection amount. As a result, it is possible to suppress adverse influence of noise caused by the unexpected changes in the air-fuel ratio on the output from the exhaust gas sensor. Further, since the degradation of the exhaust gas sensor is determined based on the output from the exhaust gas sensor delivered in a state where the adverse influence of noise caused by the unexpected changes in the air-fuel ratio on the output from the exhaust gas sensor is suppressed as described above, it is possible to enhance the accuracy of the determination of degradation of the sensor.
Preferably, the degradation determining system further comprises a bandpass filter for filtering the output from the exhaust gas sensor input thereto, such that components of the output from the exhaust gas sensor corresponding to a predetermined frequency band including a frequency of the determining input are allowed to pass therethrough, and the degradation determining means determines degradation of the exhaust gas sensor based on the output of the exhaust gas sensor, the output having been filtered by the bandpass filter.
With the arrangement of this preferred embodiment, the degradation of the exhaust gas sensor is determined based on the output from the exhaust gas sensor, which has been filtered by the bandpass filter, in other words, based on components of the output from the exhaust gas sensor within a predetermined frequency band including the frequency of the determining input. Thus, by filtering the output of the exhaust gas sensor using the bandpass filter, it is possible to eliminate noise caused by unexpected changes in the air-fuel ratio even if the noise is contained in an unfiltered output from the exhaust gas sensor. This makes it possible to determine the degradation of the exhaust gas sensor while eliminating adverse influence of the noise on the output from the exhaust gas sensor, and therefore further enhance the accuracy of the determination of degradation of the exhaust gas sensor.
Preferably, the degradation determining means determines degradation of the exhaust gas sensor based on the output from the exhaust gas sensor, after a predetermined time period has elapsed from a start of control of the amount of fuel to be injected by the control means.
With the arrangement of this preferred embodiment, the degradation of the exhaust gas sensor is determined based on an output from the exhaust gas sensor delivered after a predetermined time period has elapsed from the start of control of the fuel injection amount by the control means. This makes it possible to determine the degradation of the exhaust gas sensor based on the output from the exhaust gas sensor, after the fuel injection amount has been positively controlled by the control means, and therefore it is possible to obtain the effects provided by the above-described control of the fuel injection amount.
Preferably, the degradation determining means determines degradation of the exhaust gas sensor based on a state of changes in amplitude of the output from the exhaust gas sensor.
With the arrangement of this preferred embodiment, the degradation of the exhaust gas sensor is determined based on the state of changes in amplitude of the output from the exhaust gas sensor. As described above, the air-fuel ratio can be accurately changed with a relatively large amplitude by controlling the fuel injection amount according to the modulation output, and therefore if the exhaust gas sensor is normally operating, the output therefrom changes with an amplitude corresponding to the above amplitude of the air-fuel ratio. Therefore, as described above, it is possible to determine the degradation of the exhaust gas sensor based on the amplitude of changes in the output from the exhaust gas sensor.
Preferably, the degradation determining system further comprises cumulative value-generating means for generating a cumulative value by adding up a plurality of values of the output from the exhaust gas sensor delivered at respective different times, and the degradation determining means determines degradation of the exhaust gas sensor based on the generated cumulative value.
With the arrangement of this preferred embodiment, the degradation of the exhaust gas sensor is determined based on a cumulative value obtained by adding up a plurality of outputs from the exhaust gas sensor delivered at respective different times. As a result, when noise caused by unexpected changes in the air-fuel ratio is temporarily contained in the output from the exhaust gas sensor, it is possible to determine the degradation of the exhaust gas sensor while more effectively eliminating the adverse influence of the noise on the output from the exhaust gas sensor, thereby enabling accurate determination of the degradation of the exhaust gas sensor.
Preferably, the control means controls the amount of fuel to be injected according to a value obtained by adding together the modulation output generated by the modulation output-generating means and a predetermined value.
For example, when the air-fuel ratio of a mixture is controlled such that it becomes equal to a target air-fuel ratio, along with control of the fuel injection amount according to the modulation output, an actual air-fuel ratio sometimes becomes leaner or richer than the above target air-fuel ratio depending on characteristics of the internal combustion engine (adhesiveness of fuel, response of injectors, etc.). In such a case, the emission-reducing capability of a three-way catalyst for reducing exhaust emissions is not sufficiently exhibited, which can lead to increased exhaust emissions. According to this preferred embodiment, however, the fuel injection amount is controlled according to a value obtained by adding together the modulation output and a predetermined value, and therefore by setting the predetermined value in advance to such a value that compensates for a deviation of the actual air-fuel ratio from the target air-fuel ratio, as described above, it is possible to prevent the exhaust emissions from being increased due to the deviation. This makes it possible to maintain excellent exhaust emission characteristics during execution of the degradation determining process.
Preferably, the exhaust gas sensor is an air-fuel ratio sensor that outputs a signal indicative of a sensed concentration of oxygen contained in the exhaust gases, and the degradation determining system further comprises correction means for correcting the amount of fuel to be injected in response to the output from the air-fuel ratio sensor.
With the arrangement of this preferred embodiment, the fuel injection amount is corrected in response to the output from the air-fuel ratio sensor, whereby even when the actual air-fuel ratio is deviated toward the leaner side or the richer side with respect to the target air-fuel ratio due to the characteristics of the engine, as described above, this deviation can be controlled. This makes it possible to prevent the exhaust emissions from being increased due to the deviation.
To attain the above object, in a second aspect of the present invention, there is provided a degradation determining method of determining degradation of an exhaust gas sensor based on an output from the exhaust gas sensor, the exhaust gas sensor outputting a signal indicative of an amount of a predetermined component contained in exhaust gases emitted from an internal combustion engine into an exhaust passage thereof,
the degradation determining method comprising the steps of:
generating a determining input for determining degradation of the exhaust gas sensor;
generating a modulation output by modulating the generated determining input, using any one of a xcex94xcexa3 modulation algorithm, a xcexa3xcex94 modulation algorithm, and a xcex94 modulation algorithm;
controlling an amount of fuel to be injected into the engine, according to the generated modulation output; and
determining degradation of the exhaust gas sensor based on the output from the exhaust gas sensor delivered when the amount of fuel to be injected is controlled in the controlling step.
With the arrangement of the degradation determining method according to the second aspect of the invention, it is possible to obtain the same advantageous effects as provided by the first aspect of the present invention.
Preferably, the degradation determining method further comprises the step of inputting the output from the exhaust gas sensor to a bandpass filter to thereby perform filtering such that components of the output from the exhaust gas sensor corresponding to a predetermined frequency band including a frequency of the determining input are allowed to pass therethrough, and the degradation determining step includes determining degradation of the exhaust gas sensor based on the output of the exhaust gas sensor, the output having been filtered by the bandpass filter.
Preferably, the degradation determining step includes determining degradation of the exhaust gas sensor based on the output from the exhaust gas sensor, after a predetermined time period has elapsed from a start of control of the amount of fuel to be injected in the controlling step.
Preferably, the degradation determining step includes determining degradation of the exhaust gas sensor based on a state of changes in amplitude of the output from the exhaust gas sensor.
Preferably, the degradation determining method further comprises the step of generating a cumulative value by adding up a plurality of values of the output from the exhaust gas sensor delivered at respective different times, and the degradation determining step includes determining degradation of the exhaust gas sensor based on the generated cumulative value.
Preferably, the controlling step includes controlling the amount of fuel to be injected according to a value obtained by adding together the modulation output generated in the modulation output-generating step and a predetermined value.
Preferably, the exhaust gas sensor is an air-fuel ratio sensor that outputs a signal indicative of a sensed concentration of oxygen contained in the exhaust gases, and the degradation determining method further includes the step of correcting the amount of fuel to be injected in response to the output from the air-fuel ratio sensor.
With the arrangements of these preferred embodiments, it is possible to obtain the same advantageous effects as provided by the corresponding preferred embodiments of the first aspect of the present invention.
To attain the above object, in a third aspect of the present invention, there is provided an engine control unit including a control program for causing a computer to perform a degradation determining process for determining degradation of an exhaust gas sensor based on an output from the exhaust gas sensor, the exhaust gas sensor outputting a signal indicative of an amount of a predetermined component contained in exhaust gases emitted from an internal combustion engine into an exhaust passage thereof,
wherein the program causes the computer to generate a determining input for determining degradation of the exhaust gas sensor, generate a modulation output by modulating the generated determining input, using any one of a xcex94xcexa3 modulation algorithm, a xcexa3xcex94 modulation algorithm, and a xcex94 modulation algorithm, control an amount of fuel to be injected into the engine, according to the generated modulation output, and determine degradation of the exhaust gas sensor based on the output from the exhaust gas sensor delivered when the program causes the computer to control the amount of fuel to be injected based on the generated modulation output.
With the arrangement of the engine control unit according to the third aspect of the invention, it is possible to obtain the same advantageous effects as provided by the first aspect of the present invention.
Preferably, the program causes the computer to input the output from the exhaust gas sensor to a bandpass filter to thereby cause the bandpass filter to perform filtering such that components of the output from the exhaust gas sensor corresponding to a predetermined frequency band including a frequency of the determining input are allowed to pass through the bandpass filter, and when the program causes the computer to determine degradation of the exhaust gas sensor, the program causes the computer to determine degradation of the exhaust gas sensor based on the output of the exhaust gas sensor, the output having been filtered by the bandpass filter.
Preferably, when the program causes the computer to determine degradation of the exhaust gas sensor, the program causes the computer to determine degradation of the exhaust gas sensor based on the output from the exhaust gas sensor, after a predetermined time period has elapsed from a start of control of the amount of fuel to be injected based on the generated modulation output.
Preferably, when the program causes the computer to determine degradation of the exhaust gas sensor, the program causes the computer to determine degradation of the exhaust gas sensor based on a state of changes in amplitude of the output from the exhaust gas sensor.
Preferably, the program causes the computer to generate a cumulative value by adding up a plurality of values of the output from the exhaust gas sensor delivered at respective different times, and when the program causes the computer to determine degradation of the exhaust gas sensor, the program causes the computer to determine degradation of the exhaust gas sensor based on the generated cumulative value.
Preferably, when the program causes the computer to control the amount of fuel to be injected based on the generated modulation output, the program causes the computer to control the amount of fuel to be injected according to a value obtained by adding together the modulation output and a predetermined value.
Preferably, the exhaust gas sensor is an air-fuel ratio sensor that outputs a signal indicative of a sensed concentration of oxygen contained in the exhaust gases, and the program causes the computer to correct the amount of fuel to be injected in response to the output from the air-fuel ratio sensor.
With the arrangements of these preferred embodiments, it is possible to obtain the same advantageous effects as provided by the corresponding preferred embodiments of the first aspect of the present invention.
The above and other objects, features, and advantages of the present invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings.